Quinolones are broad-spectrum, high performance and low toxicity synthetic drugs. Early quinolones have potent activity against gram-negative bacteria, but inferior activity against gram-positive bacteria. Although newly available quinolones such as gatifloxacin (Drug, 1999, 58(4):683) and moxifloxacin (World Notes on Antibiotics, 2002, 23(6):274) exhibit improved antibacterial activity, the activity against gram-positive bacteria, and certain bacteria such as S. pneumoniae, enterococcus, etc., needs to be further strengthened. With introduction of difluoromethoxy group at C-8 position of quinolone core, T-3811, a novel quinolone with hydrogen atom at C-6 position of quinolone core (Chinese New Drugs Journal, 2002, 11(10):766), which entered phase III clinical trial in 2001, exhibits enhanced in vitro activity against S. pneumoniae, even superior to gatifloxacin.